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  1. Subscribersonhouse
    Fast and Curious
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    19 Jan '17 22:55
    https://phys.org/news/2007-05-hyper-accurate-clocks-heart-galileo.html#nRlv

    Looks like some of them failed after put in geosync orbit. The strange thing to me is Apollo timing had a cesium beam clock (Hewlett Packard's) as primary and Rubidium as secondary and temp controlled quartz clock as tertiery.

    The Euro ones use as primary, the hydrogen maser clock which was just coming online when I was on Apollo, accurate to a second in a couple million years. But the Rubidium clocks are much less accurate than the cesium clocks Apollo used as primary, accurate to a second in a hundred years or so.

    Wonder why they didn't use cesium beam clocks which are accurate to one second in about 3000 years, use that as secondary.

    Maybe it was money, go the cheapest route. Good to see hydrogen masers in use now though. It will make for much more accurate GPS readouts.
  2. SubscriberKewpie
    since 1-Feb-07
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    19 Jan '17 23:28
    It's always interesting to see the hugely expensive hi-tech stuff filter down to the rest of us. Remember the first mobile phones?
  3. Subscribersonhouse
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    20 Jan '17 13:18
    Originally posted by Kewpie
    It's always interesting to see the hugely expensive hi-tech stuff filter down to the rest of us. Remember the first mobile phones?
    Oh yeah, giant beasts with huge antennae sticking out. The cesium beam atomic clock has just been made about the size of a cube of sugar so atomic watches won't be too far in the future, now 'atomic' watches means they have to have a radio to pick up the WWV signal from Fort Collins Colorado, a frequency of 60 kilohertz, very low frequency much lower than the AM radio band. If you made a half wave antenna for that frequency it would be about 1.5 miles long or 2 kilometers. My watch has an antenna the size of a matchstick so it's not very sensitive, only picks up WWV maybe a couple times a month. That is enough though to keep it very accurate. Another extremely accurate clock is the ones on cell phones, they keep right up with WWV because they are tied to them but I think through hard wires and all the cell phone towers are synced timewise like the GPS satellites.

    BTW, GPS satellites have to have relativity equations built in because time flow varies the higher you go in altitude and the faster you go so they need to process a lot of information in order to give your GPS the right positional data. If they did not take into account relativity, they would be off by about 3 kilometers, not very useful.
  4. Subscribermoonbus
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    20 Jan '17 18:42
    You might find that the choice of clocks depended more on the contractors' offers than on the technologies involved. Just a guess.
  5. Unknown Territories
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    21 Jan '17 01:21
    Originally posted by sonhouse
    https://phys.org/news/2007-05-hyper-accurate-clocks-heart-galileo.html#nRlv

    Looks like some of them failed after put in geosync orbit. The strange thing to me is Apollo timing had a cesium beam clock (Hewlett Packard's) as primary and Rubidium as secondary and temp controlled quartz clock as tertiery.

    The Euro ones use as primary, the hydrogen maser c ...[text shortened]... Good to see hydrogen masers in use now though. It will make for much more accurate GPS readouts.
    What they were doing didn't require a high degree of accuracy.
  6. Subscribersonhouse
    Fast and Curious
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    21 Jan '17 07:08
    Originally posted by FreakyKBH
    What they were doing didn't require a high degree of accuracy.
    Tell me what they were doing then. And who are they you are talking about?
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